1. Field of the Invention
The present invention relates to an apparatus for cleaning the outer peripheral surface of a cylinder or a roller such as a cylinder of a printing machine. More particularly, the present invention is concerned with an apparatus suitable for cleaning an impression cylinder of an offset printing machine which has a projection projecting from the outer peripheral surface thereof.
2. Description of the Prior Art
Although the following description is concentrated specifically on an apparatus for cleaning a cylinder of an offset printing machine, it is to be understood that the same printing cylinder cleaning apparatus can be used for cleaning cylinders of other types of printing machine, other various cylinders or rollers.
An offset printing machine usually has three cylinders, namely, a plate cylinder, a blanket cylinder and an impression cylinder. These cylinders are arranged such that their axes extend in parallel with one another and such that they can be brought into mutual contact. A printing plate made of zinc or aluminum is wound on the plate cylinder, while a thin sheet-like blanket such as of rubber is wound on the blanket cylinder. The printing plate has a grained surface and is provided with a water repellent layer carrying an image of characters or a picture. The surface of the printing plate other than portions having images of characters or picture is dampened as water is supplied to the surface of the printing plate by means of dampening device. An oily ink is applied to the surface of the printing plate by means of an inking device. The ink will attach to the portion of the plate surface carrying the image because this area is not dampened, but will be repelled by other portions of the plate surface due to the water content held by the grained surface. The ink thus held on the plate cylinder is transferred to the blanket and is further transferred to a printing paper which passes through the nip between the blanket cylinder and the impression cylinder. This is the principle of offset printing.
The impression cylinder is provided in the outer peripheral surface thereof with a dent which extends in the direction of axis thereof. A plurality of grippers are disposed in this dent so as to partially project from the outer peripheral surface of the impression cylinder. In operation, these grippers grip and feed a printing paper sheet one by one.
The printing machine has a cylinder cleaning apparatus which has a cleaning cloth supply roll and a cleaning cloth take-up roll arranged in a pair on a pair of side plates which are mounted on the frame of the printing machine. A continuous cleaning cloth is wound at its both ends on these rolls and are suitably tensed between these rolls. The cleaning cloth take-up roll is driven by a driving device to rotate at a predetermined speed and intermittently. A stay having a substantially T-shaped cross-section is provided to extend in the direction of axes of these rolls. Both ends of the stay are fixed to the adjacent side plates. The portion of the stay opposing to the blanket cylinder is made hollow, and the surface facing the blanket cylinder is hermetically lined with a pressure pad made of an elastic member. A plenum chamber which is defined by the end of the stay and the pressure pad is communicated with an external air compressor. As the air compressor operates, compressed air is supplied to the plenum chamber so that the pressure pad is expanded, whereby the cleaning cloth sliding on the outer surface of the pressure pad is pressed against the blanket cylinder so as to wipe off contaminant on the blanket wound on the blanket cylinder thereby cleaning the blanket surface.
In the cylinder cleaning apparatus of the kind above described, the cleaning cloth is positioned away from the outer peripheral surface of the blanket cylinder when the cleaning is not conducted, and is pressed onto the surface of the blanket cylinder in response to a cleaning start signal. The cleaning cloth is held in contact with the blanket cylinder while the blanket cylinder rotates a number which is large enough to ensure sufficient cleaning of the cylinder surface. This cleaning apparatus, however, cannot be used in the cleaning of the impression cylinder, because of the presence of the grippers which partially project beyond the surface of the impression cylinder. Namely, the cleaning cloth interfere with the grippers each time the grippers are brought to the position of the cleaning cloth so as to cause the pressure pad and the grippers to be damaged. For these reasons, the cleaning of the impression cylinder requires that the printing machine is stopped to enable the cylinder surface to be manually cleaned by means of, for example, a waste cloth impregnated with a cleaning oil. Thus, the cleaning of cylinder surfaces with projections, which rely upon manual work, requires much time and labor.